What this means is that if you play a game in full-screen, the GPU settings are probably set by default to dedicate all the power to make your gaming experience as smooth as possible. Thus, making the screen on your second monitor black while you are gaming on the primary monitor.
Why is second monitor going black?
The most common reason for the second monitor going black might be the wrong cable connection or other cable issues. What is this? Some of the monitors come with many input choices so it needs you to choose the cable and port you want to use, such as HDMI 1, HDMI 2, DisplayPort 1.4, USB-C, and so on.
Why does my monitor turn black when I play games?
The black screen often appears due to graphics card problems If your screen goes black when gaming, it might indicate a serious problem with your hardware and software. Using a system restoration software will quickly get rid of the Black Screen while gaming.